LP propane or natural gas fueled heaters such as patio heaters are available in both free-standing and built-in configurations, and are primarily sold for commercial applications. For example, patio beaters have become especially popular in recent years in areas such as the Southwest where no smoking laws are being applied to taverns and bars forcing patrons outdoors to smoke which can be especially inconvenient during cold nights. Patio heaters can be utilized to provide warmth in preselected outdoor areas making it much more comfortable for smokers, and for those who like to be outdoors.
Free-standing patio heaters that can be readily moved from location to location to heat preselected areas typically have a base that is sized to contain a fuel tank therein and an elongate hollow support standard or post projecting upward therefrom to a burner assembly housing in which air is heated by combustion of the fuel gases from the tank in the base. The burner assembly housing has an emitter comprised of a cylindrical wall provided with apertures to provide for the escape of the hot gaseous products of combustion in the housing. The flow of hot gases through the wall apertures heats the wall so that the wall emits radiant heat. A relatively large dome-shaped reflector hood is attached on top of the housing and opens downwardly for reflecting heat emanating from the housing generally downwardly about the standard of the patio heater. In the built-in configuration which typically will not be moved after the unit is installed, the heater is connected to a source of gas, such as provided by a gas utility company, thus eliminating the need for the base so that the standard extends all the way from the ground up to the burner assembly housing. In each of the free-standing and built-in configurations, the burner assembly housing and reflector dome have substantially the same construction.
A shortcoming of patio heaters using apertured emitters is their relatively poor heating efficiency. Currently, about ten percent of the input energy in these patio heater is converted to infrared heat energy. Generally, the burner flames and the hot gaseous combustion products generate heat, and the current emitter heads are not in heat conducting relation with these heat sources for sufficient time as the heat energy passes through the apertured walls thereof. In other words, the apertured walls lacked sufficient surface area in optimized heat transfer relation with the heat generated by the burner assembly. Even in prior elongated and fluted solid heater casing constructions, see U.S. Pat. No. 2,950,713 to Sterick, the hot gaseous flow is not well confined for maximized heat transfer to the casing. In addition, heat is lost to the interior of the casing in the '713 patent further reducing heat transfer efficiencies. Accordingly, the heater of the '713 patent is not well-suited for high efficiency heating operations.
In conventional patio heaters, the apertures included in the cylindrical wall of the emitter have been included in an effort to provide adequate transmission of heat from the hot combustion gases to the emitter walls so that it can heat up and radiate heat to the surroundings. Although the apertured cylindrical walls on conventional heaters generate some radiant heat upon being heated up by the passing burner gases, the amount is relatively limited in reality.
The poor heating efficiency is attributable in part to the use of stainless steel and the like as the structural material of the apertured emitter wall of the conventional patio heaters. What has not been previously appreciated is that such emitters generate radiant heat predominantly at relatively shorter wavelengths of the electromagnetic spectrum that are not very efficient for heating bodies and or apparel worn by people in the vicinity of the patio heater. Stainless steel, when heated in conventional patio heaters, gives off a noticeably visible bright orange-colored glow, corresponding to considerable radiant energy being released at relatively shorter wavelengths of the electromagnetic spectrum. The rainbow of colors commonly referred to as visible light falls in the portion of the electromagnetic spectrum with wavelengths of 400 nm to 700 nm. However, it has not been previously appreciated that the radiant energy generated by the heated stainless steel emitters includes only a small proportion falling in longer wavelength bands, such as far infrared waves. For instance, it was not previously appreciated that only about 10% of the radiant energy of conventional patio heaters made with apertured stainless steel emitters is in the infrared (IR) region.
Infrared radiation is the region of the electromagnetic spectrum that extends from the visible region (0.7 μm) to 1000 μm in wavelength. Infrared waves are invisible to the human eye. Infrared waves include thermal radiation. For instance, burning charcoals may not give off visible light, but they do emit infrared radiation which is felt as heat by human skin. Radiant energy in the far infrared band (10 μm to 1000 μm), in particular, is high in such thermal radiation.
As another drawback associated with conventional patio heaters, the apertured emitters used in conventional patio heaters have poor wind tolerance. In particular, the emitter burner flame in conventional patio heaters gets extinguished by wind or even a slight breeze of sufficient strength entering the emitter housing through the grid holes of the conventional radiant emitter grid component. This leads to the loss of the heating effect until the burner flame can be re-ignited. The cost of many conventional patio heaters has been increased due to the necessity of equipping them with automatic shut-off mechanisms for handling inadvertent occurrences of flame-out at the burner assembly. As can be appreciated, a need also has existed for a more wind tolerant patio heater.
Accordingly, a need exists for a heater with increased heating efficiency. Moreover, a need also exists for a patio heater type heating apparatus, which can deliver a desired amount of heating at lower energy costs. Further, there is a need for a more wind tolerant patio heating apparatus.